Container

ABSTRACT

The container covers stack together in two different ways. First, the covers can be stacked into an “aligned” stack. The aligned stack provides structural rigidity for bulk handling during manufacturing. Second, the covers can be stacked into a “locked” stack. The locked stack provides even more structural rigidity than does the aligned stack and is useful when storing unused covers. The container cover includes a first closure portion, an engagement portion, and an alignment portion. The base includes a second closure portion. The first closure portion of the cover is sealingly engageable with the second closure portion of the base to define a sealed storage area. The alignment portion of the cover is engageable with the alignment portion of a second cover to form an aligned cover stack. The engagement portion of the cover is engageable with the engagement portion of a second cover to form a locked cover stack.

This application is a continuation of U.S. application Ser. No. 11/559,527, filed Nov. 14, 2006, which is a continuation in part of International Application No, PCT/US 06/06263, filed Feb. 22, 2006, which claims benefit of U.S. Provisional Application No. 60/655,830, filed Feb. 23, 2005.

FIELD OF THE INVENTION

The present invention relates generally to containers, and, more particularly, to containers whose covers align together when stacked in a first position and which can be locked together in a second position.

BACKGROUND OF THE INVENTION

Rigid, thermoplastic food containers are generally known. Users often accumulate a large number of these containers in different sizes and shapes. When not in use, the containers are often stored haphazardly into drawers. In this case, the unused containers take up a great deal of room, and finding a matching base and cover in a disarranged drawer may be difficult. To avoid this, some users stack the containers in cabinets. While the bases of the containers usually nest and therefore take up less room than in a disorganized drawer, it may still be difficult to match a base with a cover. In addition, the covers may not stack and the covers may tend to topple down. When the containers are in use to store food, the containers are often stacked one on top of another in cabinets or in a refrigerator. These stacks may be precarious, and their fall may cause food to spill from the containers. Many users would find it desirable if the containers, whether empty or in use, could be stored in a manner space efficient, less precarious, and more structurally rigid.

During large-scale manufacturing, the covers may be transported in bulk before being separated out for individual packaging. During bulk handling, manufacturers would find it desirable if the covers would form a stack stable enough to resist the vertical and lateral movements caused by forces typically encountered during manufacturing operations.

The present invention has as a general aim to provide containers that satisfy both users and manufacturers.

SUMMARY OF THE INVENTION

In view of the foregoing, the present invention provides containers whose covers can be stacked together in two different ways. First, the covers can be stacked into an “aligned” stack. The aligned stack provides enough structural rigidity for bulk handling during manufacturing. Second, the covers can be stacked into a “locked” stack. The locked stack provides even more structural rigidity than does the aligned stack and is useful when storing unused covers.

In some embodiments, the container cover includes a first closure portion, an engagement portion, and an alignment portion. The base includes a second closure portion. The first closure portion of the cover is sealingly engageable with the second closure portion of the base to define a substantially sealed, leak-proof, and re-sealable storage area for items such as food. The alignment portion of the cover is engageable with the alignment portion of a second cover to form an aligned cover stack. The engagement portion of the cover is engageable with the engagement portion of a second cover to form a locked cover stack.

The covers and bases can be economically constructed from relatively thin-gauge plastic so that the user can either wash them after use or dispose of them with the view that their purchase price allows them to be used as a consumable good. The container can be readily manufactured, for example, with conventional thermoforming equipment. The cover can be made from a semi-transparent material to ensure satisfactory visibility of the container's contents. The container can be suitable for refrigerator, freezer, microwave, and machine dishwasher use.

The features of the present invention will become apparent to one of ordinary skill in the art upon reading the detailed description, in conjunction with the accompanying drawings, provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a container with a cover and a base according to an embodiment of the present invention;

FIG. 2 is an isometric view of the container cover of FIG. 1;

FIG. 3 is a top plan view of the container cover of FIG. 1;

FIG. 4 is an isometric view of the container base of FIG. 1;

FIG. 5 is a top plan view of the container base of FIG. 1;

FIG. 6 is a side sectional view of the container of FIG. 1;

FIG. 7 is an enlarged, detail view of a portion of FIG. 6;

FIG. 8 is side sectional view of another embodiment of the container shown in FIG. 7;

FIG. 9 is a side sectional view of another embodiment of the container shown in FIG. 7;

FIG. 10 is a side sectional view of a stack of two sealed containers;

FIG. 11 is a side sectional view of a stack of two nested container bases with two locked container covers;

FIG. 12 is a side sectional view of another embodiment of the stack of FIG. 11;

FIG. 13 is a side sectional view of a stack of two nested container bases with one locked container cover and with one aligned cover;

FIG. 14 is a side sectional view of another embodiment of the stack of FIG. 13;

FIG. 15 is a side sectional view of an aligned stack of a container cover and a base;

FIG. 16 is a side sectional view of a stack of two nested container bases with two aligned container covers;

FIG. 17 is a side sectional view of a stack of two nested container bases with one aligned container cover and with one locked container cover;

FIG. 18 is a side sectional view of a locked stack of two container covers;

FIG. 19 is an enlarged, detail view of a portion of FIG. 18;

FIG. 20 is a side sectional view of an aligned stack of two container covers;

FIG. 21 is an enlarged, detail view of a portion of FIG. 20;

FIG. 22 is a process flow diagram of an exemplary manufacturing process for making containers according to the present invention; and

FIG. 23 is a process flow diagram of another exemplary manufacturing process for making containers according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Turning to the drawings, wherein like reference numerals refer to like elements, a first embodiment of the present invention is illustrated in FIGS. 1 through 5. A container 100 includes a flexible cover 102 sealingly engaged to a base 104. In the example of FIGS. 1 through 5, the container 100 is depicted as substantially square with rounded corners. In other embodiments of the present invention, the container 100 has other shapes such as rectangular, circular, or elliptical.

The container cover 102 can include at least one gripping tab 106 to facilitate removal of the cover 102 from the container base 104. In some embodiments, the gripping tab 106 includes one or more cross-ribs or a textured surface to improve a user's grip on the tab 106.

The container cover 102 illustrated in FIGS. 2 and 3 includes an engagement portion 200 that allows the cover 102 to engage with the engagement portion 200 of a second cover 102 to form a locked stack of covers 102. This locking feature makes the resultant stack of covers more structurally rigid and thus less precarious than a traditional, non-interlocked, stack of covers.

The engagement portion 200 of FIGS. 2 and 3 is depicted as circular but, as with the shape of the container 100 itself, other shapes are possible. In some embodiments, a standard shape and configuration of the engagement portion 200 is used with covers 102 of various shapes and sizes. This enhances storage flexibility by allowing different types of covers 102 to be stored together in a locked stack. The engagement portion 200 can also be chosen to have a shape or otherwise include elements that provide an aligned or locked stack of covers 102 with rotational alignment where rotation is defined about an axis normal to the point 302 at which midlines 304 and 306 of the cover 102 intersect as shown in FIG. 3. For instance, shapes that inherently require alignment prior to engagement or that may be self-aligning during the process of connecting engagement portions would be shapes with linear or curvilinear sides, vertices or lobes such as triangular, square, rectangular, or multi-petal shapes. Additionally, the cover may have one or more elements on or about the engagement portion that require alignment prior to connection of engagement portions or elements that may be self-aligning during the process of connecting engagement portions.

The container cover 102 may have a central field 300, shown in FIG. 3 on the top of the engagement portion 200. The central field 300 may include an embossed symbol such as a manufacturer's mark or may allow a user to attach a label or to write information, such as the date or user's name. When the central field 300 includes a writeable area, that area could be of an opaque color which would receive a contrasting color from a writing instrument. The writeable area could be incorporated into the material for the container cover 102 or could be applied to that material by printing.

The container cover 102 of FIGS. 1 through 3 can be constructed with a wall thickness thinner than that of a container base 104. The cover 102 can be made from any suitable plastic and can be made by any suitable technique, such as thermoforming. In one embodiment, the cover 102 can be formed from polypropylene. Due to the thermoforming process, the wall thickness of the cover 102 can vary. A thinner container cover 102 reduces material costs and increases flexibility to more easily accommodate its removal from, and engagement with, a container base 104. The cover 102 can maintain adequate flexibility for proper sealing even during typical freezer temperatures.

The container base 104 of FIGS. 4 and 5 includes a bottom 400 and a sidewall 402 extending from the periphery of the bottom 400. The bottom 400 includes a raised lower section 404 to accommodate the engagement portion 200 of a container cover 102 when containers 100 are stacked together. This feature is further discussed and illustrated below. Just as the engagement portion 200 of FIG. 3 can include a central field 300, a similar field for a manufacturer's mark or for user information could be included in the raised portion 404 of the base 104.

The container base 104 of FIGS. 1, 4, and 5 can be made from any suitable plastic with sufficient thickness to withstand without deforming the heat of microwave cooking and of top-shelf dishwashing. It should also remain sturdy during lifting while laden with hot food. The base 104 can be made from any suitable plastic and can be made by any suitable technique, such as co-extrusion, lamination, injection molding, thermoforming, or overmolding. In one embodiment, the container base 104 is formed from polypropylene. The wall thickness of the container base 104 can vary due to the manufacturing process.

FIGS. 6 through 9 present embodiments of a container 100 whose cover 102 is sealingly engaged with its base 104. FIG. 6 shows the cover 102 cooperating with the base 104 to define a sealed storage compartment 600. The cover 102 can be sufficiently flexible to allow a user to create a vacuum in the container 100 upon sealing. In order to create a vacuum, the user could, for example, depress the cover 102 during the closing of the container 100. A return force imparted upon the cover 102 by the resiliency of the material of the cover 102 will urge the cover 102 to return to its normal position, thereby creating a vacuum. To facilitate convenient sealing engagement of the cover 102 with its base 104, the users can, at their discretion, apply downward force to only the engagement portion 200 of the container cover 102. The engagement portion 200 is located to accept and distribute the force to the first closure portion 700 of the cover 102 during sealing to the base 104. The engagement portion 200 may also act as a convenient handle for grasping the cover 102.

In the embodiments of FIGS. 6 through 9, the container 100 uses a locking rim design that includes both inside and outside seals as will be described. The present invention can be embodied with a variety of closure designs including outer closures and/or inner closures.

FIG. 7 depicts an embodiment of the closure portions used to engage the cover 102 with the base 104 of the container 100. The cover 102 includes a first closure portion 700 in the form of a raised locking ring. The first closure portion 700 of the cover 102 can be engaged with a second closure portion 702 of the base 104 to provide a leak-resistant, re-sealable closure.

The first closure portion 700 includes an inner wall 704, a retention bead 706, and an outer wall 708. The inner wall 704, the retention bead 706, and the outer wall 708 define a first sealing surface, which is part of the lower surface of the cover 102. The first closure portion 700 can include one or more locking ridges 710. The outer wall 708 extends between the retention bead 706 and a flange 712. The flange 712 can provide a convenient gripping surface to facilitate the removal of the cover 102 from the base 104.

As illustrated in FIG. 7, the second closure portion 702 of the base 104 is a raised locking ring that extends from an upper edge of the sidewall of the base 104. The second closure portion 702 includes an inner wall 714, a retention bead 716, and an outer wall 718. The inner wall 714, the retention bead 716, and the outer wall 718 define a second sealing surface, which is part of the upper surface of the base 104. The second closure portion 702 can include one or more locking ridges 720. The outer wall 718 extends between the retention bead 716 and a flange 722. The flange 722 can provide a convenient gripping surface to facilitate the removal of the cover 102 from the base 104.

The first and second closure portions 700 and 702 can be configured to be slightly different in size to form an interference fit therebetween. The interference fit between the first and second closure portions 700 and 702 can provide a sealing engagement between the closure portions. As a result, when the two pieces are engaged, a positive seal can be formed between the first and second sealing surfaces around the perimeters of the base 104 and of the cover 102.

The engagement of the first and second closure portions 700 and 702 can be accompanied by an audible “snap” indicating that the container is securely closed.

In the example of FIG. 7, the inner wall 704 of the first closure portion 700 of the cover 102 extends to the engagement portion 200. This engagement portion 200 includes an upper protrusion 724 and a lower protrusion 726.

In the embodiment of FIG. 7, the cover 102 includes a ridge 728 on the outer wall 708 of the first closure portion 700. FIG. 8 presents another embodiment without this ridge. In general, the first and second closure portions 700 and 702 and the engagement portion 200 shown in FIGS. 6 through 9 are examples only, and many other types of closure and engagement portions could be used with the present invention. For example, the engagement portion 200 could include complementary locking rings. As these and many other types of closure and engagement portions are well known in the art, they need not be discussed at length here.

FIG. 9 shows another embodiment of the cover. The cover 102 of FIG. 9 includes an alignment ridge 900 located on the outer wall 708 of the first closure portion 700. This alignment ridge 900 is discussed in detail below.

In FIG. 10, the sealed container 100 rests on top of a second sealed container 1000. The raised lower section 404 of the base 104 of the upper container 100 accommodates the engagement portion 200 of the cover 1002 of the lower container 1000.

FIGS. 11 and 12 show the utility of an embodiment of the invention when the containers are in storage. In the Figures, a stack of two nested container bases 104 and 1100 is joined to a locked stack of covers 102 and 1102. The lower cover 102 is sealingly engaged with the upper base 104 to form a structurally rigid stack.

In the embodiment of FIGS. 11 and 12, the two covers 102 and 1102 are locked together by their engagement portions 200. As described in relation to FIG. 7, the engagement portions 200 can each include an upper protrusion 724 and a lower protrusion 726. Each protrusion 724, 726 is convex on one side and concave on the other. The lower protrusion 726 of the upper cover 1102 fits over and receives the upper protrusion 724 of the lower cover 102, thus locking the covers 102 and 1102 together. In this manner, the covers 102 and 1102 are held together and form a structurally stable cover stack. Other embodiments of the engagement portion may include one or more of the following features to enable engagement: convex portions or ribs, concave portions or ribs, linear or curvilinear undercuts, discrete snap elements or buttons, interference fits, textured surfaces, or elements that modify surface friction or tackiness at or around the point of engagement. The engaging areas that create a locking condition can be continuous about the engagement portion or discretely segmented about the engagement portion. In some embodiments, the force required to connect the covers may differ substantially from the force required to disengage the covers. For instance, it may be beneficial during manufacturing that the force needed to connect the covers is less than the force required to separate the covers. As a result, the covers are relatively easy to connect during manufacturing, yet they will lock securely and not undesirably separate during the manufacturing process. To accomplish this, the protrusions on the engagement portion may be designed where, for a given protrusion, the upper protrusion edge comprises a gradual taper whereas the lower protrusion edge comprises a more abrupt shape. For example, in one embodiment, the shape of the protrusion may be similar to a barbed hook with gradual taper on the upper edge of the barb that would impart little resistance during engagement and with an abrupt shape on the lower edge of the barb that would impart relatively high resistance during disengagement. Conversely, it may be beneficial to design the engagement portion so that the force that needs to be applied to connect the covers is more than the force required to separate the covers, since the user may perceive that a high connecting force equates to satisfactory locking integrity, whereas a weak connecting force may lead the user to perceive that the cover stack lacks the integrity required to insure the expected organizational benefit. Thus the high connecting force provides the perceived benefit, yet a lower disengagement force does not require that the user untowardly struggle during separation of covers. To accomplish this, the protrusions on the engagement portion may be designed where, for a given protrusion, the upper protrusion edge comprises an abrupt shape whereas the lower protrusion edge comprises a more gradual taper. For example, in one embodiment, the shape of the protrusion may be a reversed barb with an abrupt shape on the upper edge of the barb that would impart relatively high resistance during engagement and with a gradual taper on the lower edge of the barb that would impart little resistance during disengagement. Furthermore, during the process where the user applies force to aligned covers in a direction normal to the general cover plane so as to lock the covers together, the engagement portion can provide tactile or audible feedback upon locking. In this way the user would sense that the covers are connected and that no further force need be applied.

The container bases 104 and 1100 are shown nested in FIGS. 11 and 12 but are not locked together. In many applications, nesting the container bases without locking them together provides sufficient structural rigidity to a stack of bases. It is possible, however, to apply the techniques of the present invention to the bases themselves and to thus provide a mechanism for locking the bases together. The same types of closure and engagement portions available for locking the covers together or for locking the covers to the bases can be adapted to locking the bases together.

The container covers 102 and 1102 of FIG. 11 include the ridge 728 described in relation to FIG. 7, while the covers in FIG. 12 do not include this feature. The ridge 728 provides a rigidifying function to the outer wall 708 and also provides a retaining ledge to assist de-nesting of covers during manufacture.

FIGS. 13 and 14 present another position for the stack of covers in FIGS. 11 and 12. The container bases 104 and 1100 are nested together and the lower cover 102 is locked onto the upper base 104. However, the upper cover 1102 is not locked to the lower cover 102. Instead, the upper cover 1102 is resting on, and aligned with, the lower cover 102. In this configuration, the two covers 102 and 1102 are said to form an “aligned” stack to distinguish it from the locked stack of FIGS. 11 and 12. The ability to form an aligned, but not locked, stack is important in manufacturing because it allows the covers to be transported in bulk before being separated out for individual packaging. The aligned stack is stable enough to resist the vertical, lateral, or rotational movements caused by forces typically encountered during manufacturing operations, but the covers are not so strongly connected that they hinder de-nesting when necessary.

The tab 106 (see FIG. 1) can be designed so that the tabs nest in an interdigitating fashion when in a stack of covers so that the covers are kept in an aligned configuration. In one embodiment, the design of the tab 106 permits stable cover-to-cover stacking in the immediate vicinity of the tab 106 in the locked state, such that a portion of the tab 106 comes to rest on a portion of the cover below it in the stack to provide resistance to further stack compression.

In the embodiment of FIG. 13, the covers 102 and 1102 align by touching in two areas. First, the engagement portions 200 of the covers 102 and 1102 each includes a lower shoulder 1300 and an upper shoulder 1302. The lower shoulder 1300 of the upper cover 1102 rests on the upper shoulder 1302 of the lower cover 102. Second, the flange 712 of the upper cover 1102 rests on the outer wall 708 of the lower cover 102. These two contact areas serve to align the covers 102 and 1102 into a stack less structurally rigid than a locked stack, but sufficiently rigid for many purposes. Comparing FIGS. 11 and 13 shows how an aligned stack can be converted into a locked and rotationally aligned stack by an application of pressure upon the stacked items. FIG. 11 shows that when force is applied to the aligned stack of FIG. 13 to create a locked stack, the flange 712 of the upper cover 1102 is pushed farther down the outer wall 708 of the lower cover 102. Cover alignment is further rigidified by the touching of covers 102 and 1102 at the inside wall of the closure portions. In the embodiment of FIG. 11, the cover inner wall 704 includes an upper shoulder 1104 located just above the uppermost locking ridge 710 and a lower shoulder 1106 located just below the lowermost locking ridge 710. Thus, in this pair of locked covers, the lower shoulder 1106 of the cover 1102 rests on the upper shoulder 1104 of the cover 102. Considering both FIGS. 11 and 13, the flange 712 that creates an aligned condition can be continuous along the perimetric path of the first closure portion 700 or discreetly segmented along the perimetric path of the first closure portion 700. Considering FIG. 12, the contacting shoulders 1104 and 1106 of the inside wall 704 that create an aligned condition between locked covers can be continuous along the perimetric path of the first closure portion 700 or discreetly segmented along the perimetric path of the first closure portion 700. In some embodiments, this alignment feature may be desirable to ensure that the connected covers are aligned rotationally about an axis normal to the center of the covers, especially when the covers include engagement portions that permit rotation between the covers. In some embodiments, if the alignment feature were absent, then the covers would be free to rotate. Free rotation could have undesirable consequences because the cover stack may be inadequately organized to facilitate manufacturing or may inadequately provide an organizational benefit to the user.

The embodiment of FIG. 14 differs from that of FIG. 13 in that the flange 712 of the upper cover 1102 does not come down far enough to touch the lower cover 102 when the covers 102 and 1102 are in an aligned stack. Variations such as those between the embodiments of FIGS. 13 and 14 can be chosen to alter the amount of rigidity present in an aligned stack. Even though the flange 712 of the upper cover 1102 does not come down far enough to touch the lower cover 102 in this less rigid aligned stack, the contact between the lower shoulder 1300 of the engagement portion 200 of the upper cover 1102 and the upper shoulder 1302 of the lower cover 102 can provide concentric or rotational alignment to assist the user in aligning the engagement portions 200 during the process of connecting covers. Comparing FIGS. 12 and 14 shows how an aligned stack can be converted into a locked and rotationally aligned stack by an application of pressure upon the stacked items. FIG. 12 shows that when force is applied to the aligned stack of FIG. 14 to create a locked stack, the cover alignment is further rigidified by the touching of covers 102 and 1102 in two areas. First, the flange 712 of the upper cover 1102 rests on the outer wall 708 of the lower cover 102. Second, the lower shoulder 1106 of the upper cover 1102 rests on the upper shoulder 1104 of the lower cover 102. In some embodiments, this alignment feature may be desirable to ensure that the connected covers are aligned rotationally about an axis normal to the center of the covers, especially when the covers may include engagement portions that permit rotation between the covers.

FIG. 15 shows that a container cover 102 can be aligned, without locking, onto the top of a container base 104. FIG. 16 shows an aligned stack of two covers 102 and 1102 on top of a nested stack of bases 104 and 1100. FIG. 17 differs from FIG. 16 in that the upper cover 1102 is locked onto the lower cover 102. Comparing FIGS. 16 and 17 shows how an aligned stack can be converted into a locked stack by an application of pressure upon the stacked items.

FIG. 16 also shows another embodiment of the alignment portion of the container covers 102 and 1102. An alignment ridge 900 is located on the outer wall 708 of the covers 102 and 1102. When in an aligned stack, the flange 712 of the upper cover 1102 rests on the alignment ridge 900 of the lower cover 102 increasing the rigidity of the stack. FIG. 17 shows that when pressure is applied to the aligned stack to create a locked stack, the flange 712 of the upper cover 1102 is pushed past the alignment ridge 900 of the lower cover 102.

FIGS. 18 and 19 emphasize the compactness of a locked stack of container covers 102 and 1102, while FIGS. 20 and 21 emphasize the compactness of an aligned stack of container covers. While the aligned stack is not quite as compact as the locked stack, the compactness of either stack is a significant benefit of the present invention when covers are stored for future use.

A high-level abstraction of an exemplary manufacturing process usable for making containers according to the present invention is shown in FIG. 22. Extruded sheets of plastic (step 2200) are thermoformed into rough bases (step 2202). The extra plastic is trimmed from the rough bases (step 2204), and the completed bases are then nested into a stack (step 2206) for further handling.

In parallel with the above steps, covers are made in a similar process (steps 2212 through 2218). In steps 2216 and 2218, the completed covers need not be locked together because an aligned cover stack is sufficiently rigid for bulk handing.

For packaging the completed bases and covers, an appropriate number of bases (steps 2208 and 2210) and covers (steps 2220 and 2222) are removed from their respective stacks. The bases and covers are stacked and combined with packaging materials (steps 2224 through 2228) to create an individual retail unit 2230 (which may include a number of bases and covers). The individual retail units are then packed together in bulk (step 2232) for shipment to retail outlets.

FIG. 23 presents a variation on the manufacturing process of FIG. 22. In the embodiment of FIG. 23, the bases are processed through the same steps 2200 through 2210. However, in step 2316 of FIG. 23, the covers are locked together in a stack rather than forming the aligned stack of FIG. 22's step 2216. In some manufacturing environments, increased structural rigidity makes the locked cover stack more appropriate than the aligned cover stack. The locked stack of covers is processed through steps 2318, 2220, and 2322. In step 2224 of FIG. 23, an appropriate number of locked covers are combined with bases and packaging materials to create an individual retail unit 2330.

The container can be reusable, but it can also be constructed cheaply enough that consumers see it as a disposable item, with replacement covers and bases available separately for retail sale. The base and the cover can be fabricated by thermoforming a clarified polypropylene homopolymer material. In another embodiment, the container may be fabricated by thermoforming a clarified random copolymer polypropylene material. Other plastic materials which would be suitable for fabricating the container by thermoforming include PS (polystyrene), CPET (crystalline polyethylene terephthalate), APET (amorphous polyethylene terephthalate), HDPE (high density polyethylene), PVC (polyvinyl chloride), PC (polycarbonate), and foamed polypropylene. The material used can be generally transparent to allow a user to view the contents of the container.

The container may include a visual indication of closure between the container cover and the container base. The visual indication may be a color change in the area where the cover engages the base. In one embodiment, the closure portion on the cover may be a first color and the closure portion on the base may be a second color. When the closure portions are engaged, the first and second colors produce a third color which is visible to the user to indicate that the container is sealed.

The container may include a rough exterior surface to reduce slipping and to improve grasping by the user, especially if the user's hands are wet or greasy.

The container may include a self-venting feature. The pressure in the sealed container may increase when the sealed container and contents are heated in a microwave oven. Thus, the container cover may include a self-venting mechanism which opens when the pressure in the container exceeds a predetermined value.

The container may be divided to separate foods in the container. A divider may be integral with the container or may be a separate component. Either the base only may include a divider or both the base and the cover may each include a divider. The divider located in the cover may only partially engage the divider in the base so as to provide splash protection, or it may fully engage the divider in the base to provide varying degrees of inter-compartmental leak resistance.

The container may include a strip indicating the temperature of the container and its contents.

The gripping tab can include a relieved portion that provides less interference contact with the base during the removal or engagement of the cover while still providing an adequate closure portion to maintain proper sealing of the container. The relieved portions of the gripping tab permit venting by allowing a portion of the cover to be unsealed from the base while still maintaining a seal around the remaining perimeter of the container. This feature is useful in microwave cooking where the cover prevents food from splattering onto the inside surface of the microwave while still allowing the container to vent. By using the gripping tab, less force is required to remove the cover from the base. This lower opening force also reduces the possibility of container failure from stress and fatigue. The lower opening force can improve the ability of the user to maintain control over the container components while removing the cover from the base and thus to reduce the possibility of spilling the contents stored in the container.

The use of the terms “a,” “an,” “the,” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise indicated.

While the invention is described herein in connection with certain preferred embodiments, there is no intent to limit the present invention to those embodiments. On the contrary, it is recognized that various changes and modifications to the described embodiments will be apparent to those skilled in the art upon reading the foregoing description, and that such changes and modifications may be made without departing from the spirit and scope of the present invention. Skilled artisans may employ such variations as appropriate, and the invention may be practiced otherwise than as specifically described herein. Accordingly, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the invention. Moreover, any combination of the above described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. 

1. A container comprising: a first cover comprising a first closure portion, an engagement portion, and an alignment portion, the first closure portion being sealingly engageable with a second closure portion of a base so that when the first and second closure portions are engaged with each other, the first cover and the base define a substantially sealed storage area, the engagement portion being engageable with the engagement portion of a second cover, and the alignment portion being engageable with the alignment portion of the second cover; and the base comprising a bottom, a peripheral sidewall extending from the bottom, an open top, and the second closure portion.
 2. The container of claim 1 wherein the first cover and the base comprise thermoformed plastic.
 3. The container of claim 1 wherein the first and second closure portions comprise locking rings, the locking rings of the first and second closure portions each comprising an inner wall, a retention bead, and an outer wall.
 4. The container of claim 1 wherein the first closure portion of the first cover is engageable with the first closure portion of the second cover.
 5. The container of claim 1 wherein the engagement portion comprises a rib and a detent groove and wherein the rib of the engagement portion of the first cover is engageable with the detent groove of the engagement portion of the second cover.
 6. The container of claim 1 wherein the first cover comprises a gripping tab.
 7. The container of claim 1 wherein the bottom, peripheral sidewall, and open top of the base define a cavity and wherein the base is partially insertable into the cavity of a second base.
 8. The container of claim 1 wherein the alignment portion of the first cover comprises an element selected from the set consisting of: a flange, a protrusion, and a locking ring.
 9. The container of claim 1 wherein the alignment portion of the first cover is located on the first closure portion.
 10. The container of claim 1 wherein the alignment portion of the first cover is located on the engagement portion.
 11. The container of claim 1 wherein the alignment portion of the first cover is engageable with a second alignment portion of the base.
 12. A first cover for a container, the first cover comprising: a first closure portion; an engagement portion; and an alignment portion, wherein the first closure portion is sealingly engageable with a second closure portion of a base so that when the first and second closure portions are engaged with each other, the first cover and the base define a substantially sealed storage area, wherein the engagement portion is engageable with the engagement portion of a second cover, and wherein the alignment portion is engageable with the alignment portion of the second cover.
 13. The first cover of claim 12 wherein the first cover comprises thermoformed plastic.
 14. The first cover of claim 12 wherein the first closure portion comprises a locking ring, the locking ring of the first closure portion comprising an inner wall, a retention bead, and an outer wall.
 15. The first cover of claim 12 wherein the first closure portion of the first cover is engageable with the first closure portion of the second cover.
 16. The first cover of claim 12 wherein the engagement portion comprises a rib and a detent groove and wherein the rib of the engagement portion of the first cover is engageable with the detent groove of the engagement portion of the second cover.
 17. The first cover of claim 12 wherein the first cover comprises a gripping tab.
 18. The first cover of claim 12 wherein the alignment portion of the first cover comprises an element selected from the set consisting of: a flange, a protrusion, and a locking ring.
 19. The first cover of claim 12 wherein the alignment portion of the first cover is located on the first closure portion.
 20. The first cover of claim 12 wherein the alignment portion of the first cover is located on the engagement portion.
 21. The first cover of claim 12 wherein the alignment portion of the first cover is engageable with a second alignment portion of the base.
 22. A system of container covers, the system comprising: a first cover comprising a first closure portion, an engagement portion, and an alignment portion, wherein the first closure portion is sealingly engageable with a second closure portion of a base so that when the first and second closure portions are engaged with each other, the first cover and the base define a substantially sealed storage area, and wherein the engagement portion is engageable with the engagement portion of a second cover; and a second cover comprising a first closure portion, an engagement portion, and an alignment portion, wherein the alignment portion of the first cover is engageable with the alignment portion of the second cover.
 23. The system of claim 22 wherein the first cover and the second cover each comprises thermoformed plastic.
 24. The system of claim 22 wherein the first closure portion comprises a locking ring, the locking ring of the first closure portion comprising an inner wall, a retention bead, and an outer wall.
 25. The system of claim 22 wherein the first closure portion of the first cover is engageable with the first closure portion of the second cover. 